Coronary tracking display

ABSTRACT

A method of displaying details of a coronary artery lesion in a cineangiogram, by adjusting each frame of the cineangiogram so that the lesion is continually displayed at a fixed location on a display. The remaining cardiac anatomy appears to move, in background, past a stationary arterial segment, thus making the displayed arterial segment easier to identify and to examine by medical personnel. Cineangiographic image frames are digitized and processed by a processor and the image frames are digitally shifted to place the arterial segment in substantially the same viewing location in each frame. Sequential image frames may be presented to the viewer as a stereoscopic pair, to produce pseudostereopsis. The arterial segment appears to the viewer in foreground, as if it was floating in front of the remaining cardiac anatomy. Image frames may be further processed to aid examination by medical personnel. The processor may make quantitative measurements of the cineangiogram and may display results of those measurements to aid review of the cineangiogram. Frames may be averaged to reduce quantum noise and to blur any structure noise; frames may be compared with prior cineangiograms to increase clarity or contrast. Coordinate adjustments for a cineangiogram may help guide therapeutic procedures, or may help enhance other imaging procedures such as fluoroscopy.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 08/210,569filed Mar. 18,1994, which is in turn a continuation of Ser. No.07/771,015 filed Sep. 30, 1991, now U.S. Pat. No. 5,457,728, which is inturn a continuation-in-part of Ser. No. 07/614,790 filed Nov. 14, 1990,now U.S. Pat. No. 5,054,045 in the name of the same inventors and withthe same title, all hereby incorporated by reference as if fully setforth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a coronary tracking display. Morespecifically, this invention relates to a coronary tracking displaywhich improves visibility of details of coronary artery lesions incineangiography.

2. Description of Related Art

Cineangiography for coronary arterial segments is typically done bymeans of an x-ray image. An artery is filled with a contrast material(for example, a large molecule with iodine in it, such as megluaminediatrozoate (sold under the name Renografin 76) or iohexal (sold underthe name Omnipague), and its arterial segments are examined. Medicalpersonnel may examine the shape of the inner wall of the artery and lookfor space where the contrast material would be expected to fill, butdoes not. These spaces are called "filling defects" and commonlyindicate lesions for which a specific treatment may be desireable.

It is advantageous to collect and display images of coronary arterialsegments for later review by medical personnel. For example, review ofsuch images may prove useful in detecting and locating lesions, and thusmay assist in treatment of a patient by interventional methods. However,one problem which has arisen in the art is that image quality underconditions imposed by cineangiography may be poor, making it difficultfor medical personnel to readily recognize critical features.

It may also be advantageous to insert a catheter into an artery,approach an arterial segment containing a lesion, and perform aninterventional therapy on that lesion. For examples, a lesion may bedilated with a balloon or ablated with a laser. Because these treatmentsmay shave adverse effects, it is desireable to identify which lesionstruly require treatment.

Another problem which has arisen in the art is that it may be difficultto move such a catheter within the patient's arterial network. It wouldbe advantageous to superimpose an image of the catheter on the patient'sarterial network while moving the catheter. However, the contrastmaterial may have adverse effects on the patient, so it is generally notpreferred to collect and display cineangiographic images while moving acatheter.

SUMMARY OF THE INVENTION

The invention provides a method of displaying details of a coronaryartery lesion in a cineangiogram, by (digitally or analog) adjustingeach frame of the cineangiogram so that the lesion is continuallydisplayed at a fixed location on a display. As a result, the remainingcardiac anatomy appears to move, in background, past a stationaryarterial segment, thus making the displayed arterial segment easier toidentify and to examine by medical personnel. In a preferred embodiment,cineangiographic image frames are digitized and processed by a processorand the image frames are digitally shifted to place the arterial segmentin substantially the same viewing location in each frame.

In a preferred embodiment, sequential image frames may be presented tothe viewer as a stereoscopic pair, to produce pseudostereopsis. As aresult, the arterial segment appears to the viewer in foreground, as ifit was floating in front of the remaining cardiac anatomy. Moreover,image frames may be further processed to aid examination by medicalpersonnel. The processor may make quantitative measurements of thecineangiogram and may display results of those measurements to aidreview of the cineangiogram. Frames may be averaged to reduce quantumnoise and to blur any structure noise; frames may be compared with priorcineangiograms to increase clarity or contrast. Coordinate adjustmentsfor a cineangiogram may help guide therapeutic procedures, or may helpenhance other imaging procedures such as fluoroscopy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a drawing of a cineangiographic system.

FIG. 2 shows a block diagram of a digital processing system foradjusting the image of the lesion in a cineangiogram.

FIG. 3 shows a block diagram of a digital processing system forproducing pseudostereopsis.

FIG. 4 shows a block diagram and drawing of a cineangiographic systembeing employed to aid in catheterization.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a drawing of a cineangiographic system.

A cineangiographic system 101 may comprise a table 102 on which apatient 103 is placed, with an x-ray generating tube 104 below the table102 for projecting x-rays and an x-ray intensifier tube 105 placed abovethe table for receiving x-rays. The x-ray intensifier tube 105 may becoupled to a motion-picture camera 106 or a television camera 107, whichmay produce a video image signal 108 of the patient's heart 109, as iswell known in the art. The video image signal 108 may be stored on astorage medium such as a videotape 110, and may later be retrieved anddisplayed on a video monitor 111 for review by medical personnel, as iswell known in the art.

A film 112 captured by the motion-picture camera 106 may also bedisplayed by a motion-picture projector 113 on a projection screen 114.The film image may be directed by the motion-picture projector 113 at anadjustable mirror 115, which may be disposed to reflect the film imageonto the projection screen 114.

FIG. 2 shows a block diagram of a digital processing system foradjusting the image of the lesion in a cineangiogram.

In a preferred embodiment, the video image signal 108 may be coupled toa processor system 201, which may digitize the video image signal 108and store a digital signal 202 in a memory 203. The processor system 201may then adjust each frame of the cineangiogram so that a lesion iscontinually displayed at a fixed location on a display screen.

In a preferred embodiment, the processor system 201 may comprise aprocessor, memory comprising a stored program, memory comprising data,and input/output devices, as is well known in the art. Although theoperation of the processor system 201 is given in terms of functionsthat it performs, it would be clear to one of ordinary skill in the art,after perusal of the specification, drawings and claims herein, thatmodification and/or programming of a standard microprocessor to achievethe functions disclosed herein would be a straightforward task and wouldnot require undue experimentation.

In a preferred embodiment, the processor system 201 may comprise an ADACcomputer made by ADAC Corporation, or may be a GE DXC image acquisitionsystem made by General Electric Corporation.

Collecting Data on Lesion Location

In a preferred embodiment, the processor system 201 may operateinteractively with a human operator, as is well known in the art. First,the processor system 201 may retrieve a single frame 204 of the storeddigital signal 202 from memory 203, and may display that frame 204 on anoperator's monitor 205. As each frame 204 is displayed, thedineangiogram will show a motion picture of the patient's heart 109. Inthis motion picture, an arterial segment 206 may appear on which thereis a lesion 207. However, because of the patient's heartbeat, the lesion207 will tend to move about on the screen.

A human operator 208 may examine the operator's monitor 205 and mayindicate (e.g., with a pointing device such as a light pen, mouse ortrackball) the location in the frame 204 of the lesion 207. Theprocessor system 201 may receive the indication by the operator 208 andmay store a set of spatial coordinates 209 for the lesion 207 which itassociates with the frame 204. The processor system 201 may then repeatthis interactive process for each frame 204 of the stored digital signal202. When complete, the processor system 201 will have a record storedin memory 203 of movements which the lesion 207 undergoes as a result ofthe patient's heartbeat.

In an alternative preferred embodiment, the processor system 201 maylocate the lesion 207 by edge-detection or other automatic means. Forexample, the stored digital signal 202 may comprise a set of pixels,each of which represents a measure of light level detected by thetelevision camera 107. The patient's arterial network may have adifferent light level from other structure. The processor system 201 maythen trace the patient's arterial network and determine what areas ofthe digital signal 202 represent arteries and what areas represent otherstructure.

In a preferred embodiment, the technique used by the processor system201 for edge-detection may comprise a technique based on an optimummatched filter, described in a technical appendix to this applicationand hereby incorporated by reference as if fully set forth herein. Adescription of a preferred optimum matched filter technique is alsogiven in the Ph.D. thesis of J. Martin Pfaff, on file with the UCLALibrary System, and hereby incorporated by reference as if fully setforth herein. However, it would be clear to one of ordinary skill in theart, after perusal of the specification, drawings and claims herein,that other techniques for edge-detection or for otherwise locating thelesion 207 would be workable, and are within the scope and spirit of theinvention.

In one aspect of this alternative preferred embodiment, the operator 208may identify the lesion 207 in one frame 204 by the same technique, butthe processor system 201 may determine the location of the lesion 207 inthe succeeding frames 204 automatically. For example, the processorsystem 201 may locate the lesion 207 by noting the distance from thelesion 207 to a reference point 210, such as a junction of arterialsegments, and by locating the lesion 207 in the succeeding frames 204 byreference to the reference point 210.

In another aspect of this alternative preferred embodiment, theprocessor system 201 may determine the location of the lesion 207 bynoting a point in the arterial segment where the arterial segment ismuch narrower. In this aspect, the operator 208 may identify the lesion207 of interest out of several possible lesions 207 which might bedisplayed.

Where the cineangiogram is captured on film 112, the operator 208 mayexamine the projection screen 114 and may indicate (e.g., with apointing device such as an acoustical x-y digitizer) the location on theprojection screen 114 of the lesion 207 in each frame 204 of thecineangiogram (prior to adjustment). The processor system 201 mayreceive the indication by the operator 208 and may store the set ofspatial coordinates 209 for the lesion 207 which it associates with theframe 204. The processor system 201 may then repeat this interactiveprocess for each frame 204 of the film 112. When complete, the processorsystem 201 will have a record stored in memory 203 of that motion whichthe lesion 207 undergoes as a result of the patient's heartbeat.

Further Image Processing

In a preferred embodiment, the processor system 201 may further processthe frames 204, both to aid visual examination by medical personnel andto generate medical data.

The processor system 201 may compute quantitative measurements of thecineangiogram. For example, edge detection and centerline detectionallow the processor system 201 to measure or compute the length, widthand spatial orientation of arterial segments 206, size and location oflesions 207 or other morphologies of the arterial segments 206, andrelative stenosis. The processor system 201 may also compute roughnessindex, cross-sectional area and thickness of arterial segments 206, bymethods which are well known in the art. Because data on lesion 207location is collected, the processor system 201 generally need notrecompute the location of the arterial segment 206 in each frame 204,aiding automated quantitative measurement.

Image enhancement techniques may be applied to the video image signal108 and the frames 204 altered so as to enhance their clarity. Forexample, the processor system 201 may locate the edges of arterialsegments 206, or other features such as the location and size of lesions207, and may superimpose them on the video monitor Ill when displayingthe frames 204. The processor system 201 may display quantitativemeasurements as "false color" on the video monitor 111.

In a preferred embodiment, the frames 204 may be averaged to reducequantum noise and to blur any structure noise, either for display orwhen computing quantitative measurements of the cineangiogram. In apreferred embodiment, after adjusting each frame 204 of thecineangiogram so that the lesion 207 is continually found at a fixedlocation, the processor system 201 may average the adjusted frames 204and compute quantitative measurements on the average. The average may beover a cardiac cycle of about thirty frames 204. In an alternativepreferred embodiment, the processor system 201 may compute quantitativemeasurements for each frame 204 and average the quantitativemeasurements over a cardiac cycle.

In a preferred embodiment, the frames 204 may also be processed toincrease contrast, either for display or when computing quantitativemeasurements of the cineangiogram. In a preferred embodiment, thesesteps may be performed:

(1) A first cineangiogram may be taken, with contrast material present,and each frame 204 adjusted based on the set of spatial coordinates 209which are collected for the lesion 207.

(2) A second cineangiogram is taken, this time without contrast materialpresent, and each frame 204 adjusted based on the set of spatialcoordinates 209 collected for the lesion 207 in the first cineangiogram.

(3) Each frame 204 of the second cineangiogram is subtracted, afteradjustment, from a corresponding frame 204 of the first cineangiogram,or from a corresponding frame 204 of a third cineangiogram taken withcontrast material present. Alternatively, the frames 204 of the secondcineangiogram may be averaged, after adjustment, over a cardiac cycle,and the average subtracted from every frame 204 of the firstcineangiogram.

It would be clear to one of ordinary skill in the art, after perusal ofthe specification, drawings and claims herein, that other and furthersignal processing may be performed on the stored digital signal 202,such as filtering, noise-removal and other related techniques. Suchother and further signal processing would be workable, and is within thescope and spirit of the invention.

Displaying the Lesion

The processor system 201 may then display the stored digital signal 202on the video monitor 111 for review by medical personnel. First, theprocessor system 201 may retrieve a single frame 204 from memory 203,and note the spatial coordinates 209 of the lesion 207. The processorsystem 201 may then adjust that frame 204 to place the lesion 207 in aspecified location (e.g., a position near the center of the screen).Alternatively, the processor system 201 may adjust each frame 204 exceptthe first to place the lesion 207 in the same location as in the firstframe 204. As a result, the lesion 207 appears in the same location ineach screen, and the remaining cardiac anatomy appears to move, inbackground, past a stationary arterial segment.

The processor system 201 may also display the cineangiogram, as capturedon film 112, on the projection screen 114. The processor system 201 maybe coupled to the mirror 115 and may continually adjust the position ofthe mirror 115 so as to continually adjust the reflection of the filmimage onto the projection screen 114. In particular, the processorsystem 201 may adjust the position of the mirror 115 so that the lesion207 appears in the same location on the projection screen 114 in eachframe of the film 112, in like manner as if a digital frame image hadbeen adjusted so that the lesion 207 appears in the same location ineach frame 204.

Pseudostereopsis

FIG. 3 shows a block diagram of a digital processing system forproducing pseudostereopsis.

In a preferred embodiment, the processor system 201 may present a pairof sequential frames 204 to medical personnel as a stereoscopic pair, toproduce pseudostereopsis. An odd frame 301 is displayed on a left half302 of a stereoscopic display 303, while an even frame 304 is displayedon a right half 305 of the stereoscopic display 303. When thestereoscopic display 303 is viewed with appropriate stereoscopicequipment, a three-dimensional image will appear, as is well known inthe art. As a result, the arterial segment appears to the viewer inforeground, as if it was floating in front of the remaining cardiacanatomy.

Aid in Catheterization

FIG. 4 shows a block diagram and drawing of a cineangiographic systembeing employed to aid in catheterization.

In a preferred embodiment, a catheter patient 401 may be catheterizedwith a catheter 402 which is inserted into one of the patient's arteries(typically the femoral artery), as is well known in the art. In apreferred embodiment, the catheter patient 401 may be positioned on afluoroscope 403, which generates an x-ray image 404 of the catheter 402.The x-ray image 404 may then be superimposed on a frame 204 retrievedfrom memory 203 by the processor system 201, to form a composite image405. The composite image 405 may then be adjusted so that the catheterremains in the same location in the image.

For example, the processor system 201 may simply "play back" the set ofcoordinate adjustments it made for the cineangiogram, applying thosesame coordinate adjustments to the x-ray image 404 of the catheter 402.In this aspect of the invention, movement of the image which is due tothe patient's heartbeat may be essentially eliminated, so that medicalpersonnel performing the catheterization may determine routing of thecatheter in the patient's arterial network.

In like manner, coordinate adjustments recorded for the cineangiogrammay help guide other therapeutic procedures, such as balloonangioplasty, laser angioplasty, atherectomy, stent insertion,thrombectomy, intravascular ultrasound, radiation therapy andpharmacologic agent delivery. In general, when invading the body with amoving object, the progress of that object may be viewed by means ofimages which are adjusted by the techniques described herein, so thatprogress of the moving object may be measured with reference to arelatively fixed map of the patient's body. In a preferred embodiment,these steps may be performed:

(1) A first cineangiogram may be taken, with contrast material present,and each frame 204 adjusted based on the set of spatial coordinates 209which are collected for the lesion 207. Image enhancement techniques maybe applied to enhance the clarity of the position of the arterialsegment 206 and the lesion 207.

(2) A therapeutic process may be performed with a live secondcineangiogram, this time without contrast material present. It may bequite difficult to see the arterial segment 206 or the lesion 207 in thesecond cineangiogram, so the results of image enhancement from the firstcineangiogram are used to identify them. In a preferred embodiment, eachframe 204 of the second cineangiogram may be adjusted based on the setof spatial coordinates 209 collected during the first cineangiogram. Ina preferred embodiment, the patient's electrocardiogram may be used tosyncronize the spatial coordinates 209 from the first cineangiogram withthe frames 204 in the second cineangiogram. In a preferred embodiment,the processor system 201 may indicate the edges of arterial segments206, or other features such as the location and size of lesions 207, andmay superimpose them on the video monitor 111 when displaying the frames204, as a "roadmap" for the therapeutic process.

In a preferred embodiment, steps (1) and (2) may be alternated insequence, so that a first cineangiogram is taken, then the therapeuticprocess is advanced some using the results of image enhancement, thenanother first cineangiogram is taken, then the therapeutic process isadvanced some more using the results of further image enhancement, andso on.

Other Medical Imaging Applications

It would be clear to one of ordinary skill in the art, after perusal ofthe specification, drawings and claims herein, that the techniquesdescribed herein for cineangiograms may also be applied to fluoroscopy.In the art of fluoroscopy, an x-ray generating tube (like the x-raygenerating tube 104 of the cineangiographic system 101) may be disposedfor projecting x-rays and an x-ray intensifier tube (like the x-rayintensifier tube 105 of the cineangiographic system 101) may be disposedfor receiving x-rays. The x-ray intensifier tube 105 may be coupled to adisplay (like the video monitor 111 of the cineangiographic system 101)for immediate display of an x-ray image of the patient 103.

One problem which has arisen in the art of fluoroscopy is that excessiveexposure to x-rays can put both the patient 103 and any nearby medicalpersonnel (such as those viewing the x-ray image) at risk of radiationdamage. One solution has been to generate a sequence of relatively stillx-ray images, each using only relatively short bursts of x-rays, at adisplay rate which gives the illusion of a continuous motion picture,i.e., an x-ray movie similar to a cineangiogram. It would beadvantageous to reduce exposure to x-rays, e.g., by reducing the numberof frames per second which are generated and displayed ("frame rate").However, because of the patient's heartbeat, this has the effect ofproducing an x-ray image which is jumpy and difficult to view.

Each frame of the fluoroscopic x-ray image may be adjusted by thetechniques shown herein, so that an identified feature (e.g. an arterialsegment or lesion) is continually displayed at a fixed location on thedisplay screen. Because the identified feature does not move about onthe screen, jumpiness which might be induced by a lowered frame rate isameliorated and the image is of acceptable quality. Accordingly, theframe rate may be reduced from about 30 frames per second to about 3frames per second or fewer, while maintaining acceptable visualizationof the arterial segment or lesion.

It would be clear to one of ordinary skill in the art, after perusal ofthe specification, drawings and claims herein, that the techniquesdescribed herein for cineangiograms may also be applied to other medicalimaging applications, including imaging applications which use imagingsignals other than x-rays. For example, the techniques described hereinmay also be applied to echocardiography (of several types, such asexercise, transesophageal, transthoracic, intravascular ultrasound),ultrafast computed tomography, cine magnetic resonance imaging, andsingle-photon emission computed tomography. In general, a sequence ofimages comprising a moving feature may be adjusted by the techniquesdescribed herein to continually maintain the moving feature at arelatively fixed location in the image, and the adjusted image may beused by personnel or processes which find advantage to looking to arelatively fixed location for the moving feature.

Alternative Embodiments

While preferred embodiments are disclosed herein, many variations arepossible which remain within the concept and scope of the invention, andthese variations would become clear to one of ordinary skill in the artafter perusal of the specification, drawings and claims herein.

We claim:
 1. A method of displaying a feature moving within afluoroscopic image, comprising the steps of:capturing a fluoroscopicimage over a sequence of image frames; identifying a feature movingrelative to the rest of said fluoroscopic image; and adjusting thedisplay position of each said frame so that the said feature iscontinually displayed in substantially the same viewing position on avideo display screen.
 2. A method as in claim 1, wherein said step ofidentifying a feature moving relative to the rest of said fluoroscopicimage further comprises:the step of displaying at least one of saidimage frames to an operator; and retrieving information indicating alocation of said feature from said operator.
 3. A method as in claim 2,wherein said step of identifying a feature moving relative to the restof said fluoroscopic image occurs automatically.
 4. A method as in claim3, wherein said step of automatic identification further comprises thestep of edge detection.
 5. A method of displaying a feature movingwithin an image comprising the steps of:capturing an image over asequence of image frames made in response to echocardiography, ultrafastcomputed tomography, cine magnetic resonance imaging, or single-photonemission computed tomography; identifying a feature moving relative tothe rest of said image; and adjusting the displaying position of eachsaid frame so that the said feature is continually displayed insubstantially the same viewing position on a video display screen.
 6. Amethod as in claim 5, wherein said step of identifying a feature movingrelative to the rest of said image further comprises:the step ofdisplaying at least one of said image frames to an operator; andretrieving information indicating a location of said feature from saidoperator.
 7. A method as in claim 6, wherein said step of identifying afeature moving relative to the rest of said image occurs automatically.8. A method as in claim 7, wherein said step of automatic identificationfurther comprises the step of edge detection.
 9. A system for displayinga feature moving within a fluoroscopic image, comprising:means forcapturing a fluoroscopic image over a sequence of image frames; meansfor identifying a feature moving relative to the rest of saidfluoroscopic image; and means for adjusting the display position of eachsaid frame so that the said feature is continually displayed insubstantially the same viewing position on a video display screen.
 10. Asystem as in claim 9, wherein said means for identifying a featuremoving relative to the rest of said fluoroscopic image furthercomprises:a means for displaying at least one of said image frames to anoperator; and a means for retrieving information indicating a locationof said feature from said operator.
 11. A system as in claim 10, whereinsaid means for identifying a feature moving relative to the rest of saidfluoroscopic image is automated.
 12. A system as in claim 11, whereinsaid automated means for identification further comprises a means foredge detection.